1. Field of the Invention
The present invention relates to optical transmitter devices that are used to transmit test signals across optical fibers in an optical fiber network. More particularly, the present invention relates to optical transmitter devices that are used in fiber administration systems to test the integrity of optical fibers connected to that system.
2. Description of the Prior Art
There are many applications that utilize an optical fiber network to establish optical communications between a host digital terminal (HDT) at a central office and an optical network unit (ONU) at a remote location. Since a central office serves as the point of origin for the optical fibers in the optical fiber network, equipment is used at the central office to organize various optical fibers in the optical fiber network. In certain optical networks, the optical fibers at the central office are is connected to dedicated pieces of equipment, such as optical signal transmitters, that serve only one purpose.
If the optical fibers are to be connected to another piece of equipment, such as test equipment, the optical fibers must be manually connected to that new piece of equipment.
In more sophisticated applications, optical fibers are terminated at fiber administration systems at the central office. Fiber administration systems enable many different types of equipment to be connected to the optical fibers without having to reroute the optical fibers from their point of termination.
In many fiber administration systems, as the optical fibers in a network enter the central office, they are directed into an optical distribution frame where the individual optical fibers are terminated in an organized manner. Such fiber administration systems are exemplified by the LGX.RTM. fiber administration system which is currently manufactured by Lucent Technologies of Murray Hill, N.J., the assignee herein.
Each optical distribution frame located at the central office typically defines a plurality of bays, wherein each bay houses several different types of dedicated equipment shelves. One type of dedicated equipment shelf contained within a fiber distribution system is a fiber distribution shelf. Located within fiber distribution shelves are optical connection ports that receive the ends of all of the individual optical fibers that enter the central office and are contained within the optical fiber network. By terminating each optical fiber at an optical connection port on one of the different fiber distribution shelves, the location of each optical fiber becomes known within the overall assembly. Once terminated at a known address on one of the fiber distribution shelves, each optical fiber can be selectively coupled to a variety of other types of equipment contained within other shelves of the fiber distribution system.
At the opposite end of the various optical fibers are the customers of the telecommunications provider. For customers having smaller scale telecommunications needs, the optical signals transmitted on the optical fiber network are converted to electrical signals prior to termination of the customer premises in a traditional manner. As such, the entire optical network is controlled and maintained by the telecommunications provider. However, with customers that have large-scale telecommunication requirements, it is not uncommon for the telecommunications provider to run a pair of optical fibers from the optical network directly into the customer premises. One fiber is used to receive signals from the telecommunications provider and the other fiber is used to send signals to the telecommunications provider.
In either case, the dependence upon optical fibers in today's telecommunications networks is substantial. Because of the increased dependence upon the use of optical fibers, an increased importance has also been placed on the testing and monitoring of optical fibers in order to ensure proper operation.
In the past, the testing and monitoring of optical fibers has required the deployment of a stable optical light source, i.e., a laser, which has typically been embodied in a cumbersome piece of test equipment. Output levels of the laser are typically measured via a backface monitoring technique, as would be understood to persons skilled in the art. A drawback to tracking the output laser power using only the backface monitoring technique is that this technique does not always accurately reflect the laser power which has been output over the optical fiber. This may be due, for example, to temperature variations between the optical fiber and the laser apparatus which can cause slight misalignments to occur between the optical fiber and the laser, which is sometimes referred to as creeping.
Accordingly, there is need for a more efficient and reliable manner in which to test and/or continuously monitor the integrity of optical fibers that are deployed in an optical communications network.